I found that for port 80 I needed higher privileges to see the listing: sudo lsof -i :80 -S. I would guess this is true for any restricted-use port (those at or below 1024 if I remember correctly).
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amacleodNov 18 '14 at 19:39

I ca not issue either command . I can see the man pages but when I issued the command I get a "lsof: Command not found.". Similar case with fuser also .
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GeekJan 23 '13 at 10:50

@Geek you may have to either install the packages or specify the full path depending on your setup.
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Ulrich DangelJan 23 '13 at 11:48

I have no option of installing anything on this machine . Which full path are you talking about ? How can I see it ? Can you please put that information in the answer itself ?
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GeekJan 23 '13 at 15:21

At least lsof is commonly only easily available to the system administrator, by virtue of being placed in one of the sbin directories. Try sudo -i followed by the lsof command, and see if that works better.
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Michael KjörlingJan 23 '13 at 15:32